Push-pull electric switch



Aug. 2, 1960 H. M. DREssEL PUSH-PULL ELECTRIC SWITCH Filed April 2'?, 1959 This invention relates to .Apushepull l'electric switches, and more particularly to those used in conjunction with volume controls for radios and television sets.

One of the problems in -a combined volume controll @and electric l'switch of the type 4in which the -control shaft Vis rotated -to regulate the volumeof sound and is moved Patented Aug. 2, 1960` sprling extending across the vsha-ft, thereby liniitingrforaxially in opposite directions to turn "the 'electric 'cur-rent on and oif, is that if 1a vstrong spring fis fused for snapping a movable Contact against a stationary Contact so as to make good electrical contact with 'it, the lateral pressure exerted by the spring on the shaft may create so much side thrust that an undesirable amount Iof friction .is produced. kAnother problem relates to :grounding `the control shaft. cannot be depended 'upon for rmaleing fgood "electrical connection with the shaft to ground it.' Thus, A'sensitive It has been found 'that the shaft bushing circuits connected with the volume control, -it is #found Y that if -the electrical resistance between the shaft Yand the bushing -is 4not lextremely flow, theioperatorin touching-the shaft will induce a disturbing voltage into the control circuit. When aline switch fis combined with'thecontrol, that condition becomes a 1ct worse, because it also J-is possible for the 'switch circuit to induce voltages into the sensitive volume control circuit. A

It is `among the objects fof this invention =to provide ia push-pull electric switch, .in which a `movable. Contact engages one or morestationary contacts with considerable pressure, in which side thrust on the control shaft =is jsubstantially eliminated, in which the -shait iis veffectively grounded, in which .the last two objects areaccornplished by a single additional element that also restricts outward movement of the shaft, .in which 4the :movable contact can be made self-aligning witha .pair of fixed contacts,

ward movement of the shaft. Also, it is v'desirable that the txed contact be L'shaped, with yone leg of the extending throughthe back wallof thehousing andthe other leg Y'extending' along the 'back wall'inside the housing. Y I" Thev invention fisr illustrated Ain the accompanying drawings-:in which f Fig. l `is :a rear view fof.rny=switch; g Fig. 2 is `a horizontal central section through the switch and part 'way through 'a volume Icontrol ysecured* to the front of the switch;

Fig. ElV is la `vside view "of the switch, with its 'side wall broken away to show the interior;

Figs. `4 and 5 are vertical sections taken on thev :lines IVV-IV `and V-V, respectively, of Fig. 2;

Fig. '6 Ais 1a fragmentary view similar to Fig. 2, but showing the *switch closed;

lFig. 7 is a fragmentary view of a modified switch, with 'therupper partl tof its side wall fbroken "av/ay; and Fig. 8 `is a view :looking into the back 'of the sniodiiiied switch :after the .rear wall :has `been rremoved, the positions of the fixed contacts being indicated by brokenflines.

Referring 'to 'the first six fii-gures of the drawings, :a control :shaft fl lis rotatably 'and slidably .mounted 1in a bushing 2 :secured tothe frontfof asuitable volume control un'it 3. Ffllhe bushing "is threaded :and adapted to extend lthrough a V'hole in 'a panel and Vreceive a nut -for rigidly mounting the bushing in place. The shaft'has a non=circ1ilar -central :portion f4 that :splined in a head f5 or insulating material rotatably mounted .in :the volume control housing. The rhea'd carries thefusual 'Contact (ino't shownf) that vslidablly lengages 1a y.resistance `element 6 the front of the control housing. The rear lend of "the shaft extends back through fa ce'ntraliopening 7' iin the back :of the volume control and l*on through a similar opening 3 in the :metal frontfwall i9 fof ai witch housing 'that Jyhas a 'Cylindrical -Slde Wall' -110 intgral Wit-h its flfolt wah. `The :tremor thezswitch housing gis welded for tetherwise arigidlyattachei no the back -ofithe volante control 1 housing. l

and in which the xed contacts are Vshaped Iso .that 'ex'ce'ssive solder or linx used in connecting 'wires vto th'ern cannot reach their contact faces. K

In accordance with Vthis invention a s'wit'ch Vhousing has front and 'back walls connected by la side wall. Tnefront wall has a central opening through it, in lfront of which a bushing is rigidly mounted for rotatably and fslidably supporting a control shaft lthat extendsV back into 'the housing. Preferably, the bushing is mounted 'on a volume The control shaft fextends back =`into-the Vswitch housing and, inf-its rear post-ionlisispac'eda short distance from 'the ins -ated rear wall 17,2"of thelrh'ousing. This wall support-s' a ipair of fixed contacts .1:3 *thae disposed fquite iclose l together between 'the center fof the IWallfand one side control fastened to the lfront of the v switch housing; Ifnside the switch housing there is a switch arm that is Vinclined to the shaft and that is provided with an opening which loosely -receives the vshaft extending :through it. Provision is made for oscillatably mounting @the arrnfon n of :the housing. VIVIl ia'ch contact preferably is iL-sha'ped, with one leg `ofthe L rigidly mounted in -the back wall ofy `the housing fan'd .projecting -froinlits lopposite sides. The Yother leg of :the --L is inside *the fhousing ian'd extends along 'the back Wall toward vthe Vadjacent.side fof theihousf y ingr flatter yleg y:may Tlne-curved t-ransverselyslight-ly to provide -a .convex contact surface facing the 4front l'of thev` housing., Thel shape -of these contacts tpl-events anyr v solderorrllux, which may creep walong the contacts' )into axis extending across theshaft. fcoil spring Iis"t`ensic' ned between the rear end ofthe shaft and one fend of 'the arm, With the lpoint of connection 4ofjthe -sh'aft tor the being movable by the `shaft forward from 'a `location in back of the arm axis to a location in frontofthat 'axis in order to cause the spring to snap -one 'endof the arm forward and thereby swing its opposite end backward toward the yback wall ofthe housing. electric contact is Acarried by the free end `of the arm 1to1-'engagement the housing, from reaching their contact-.surfaces. 1 Y,

In order to engagethe -ilxed contacts; one or more movable lcontacts* are provided. Y A single bridging on-A ta'ct 'I4' for engaging both 'fixed contacts simultaneously is shown. bridging Acontact is carried by one end of vran ann "A15 'that isfornied from a plate of insulating material. The isinelinedjto the lshaft `a'ini :is prewith a fixed -electric contact mounted 1in the housing in A l.spring located :in the vided with "an opening 1'6, 'through 'which the :shaft extends. The opening is considerably larger than the shaft .so that 'It-he arin will not engage it. As shown in Fig. 4,1the1opening preferably is formed gfrom two slots intersecting each other to form a T, with the cross bar of the T parallel to the bridging contact and close to it. The stern of the T extend from the opposite side of the Vcross bar toward the end of the arm remote from the contacts. Shoulders 17 are thus provided by the sides of the cross bar that connect with the stern of the opening. These shoulders are set in semicircular notches 18 (Fig. 6) in the edges of a pair of tongues 19 cut from the front wall of the switch housing and bent backwardly into parallel relation. The positions of the tongues in the ends of the cross bar of opening 16 prevent arm from moving sideways. To hold arm shoulders 17 in the tongue notches, a coil spring 20 is disposed in the stem of opening 16 and has one end hooked around the adjacent end of the arm and the opposite end hooked onto the grooved rear end of the shaft behind the arm. -In this position the spring also holds the adjoining end of the arm in its'rearposition and its free end in its forward position, which can be limited by a detent 21 pressed out of the front wall of the housing.

It will be seen that with'this construction forward movement of the control shaft to the position shown in Fig. 6 will pull the inner end of the spring forward to a location in front of notches 18 and cause the opposite end of the spring to snap the adjoining end of the arm forward and thereby swing the bridging contact back against the fixed contacts. During this movement of the arm, it swings on an axis passing through its shoulders in the tongue notches, the tongues thereby serving as bearing members for oscillation of the arm. When the bridging contact strikes the'xed contacts it will align itself with them because it is formed from a bar that has forwardly bent ends extending loosely through oversized openings 22 in the arm and then bent toward each other, and the central part of the baris provided with a rounded projection 23 (Fig. 2) that spaces the bar from the rear face of the arm. The bar can therefore rock in any direction on the projection to accommodate itself to the xed contacts in order to bear against both of them with equal pressure. When the shaft is pushed in again, the coil spring will snap the arm in the opposite direction to swing the bridging contact away from the fixed contacts, as shown in Fig. 2.

It is a feature of this invention that the coil spring can be made as strong as desired in order to hold the bridging contact tightly against the xed contacts. This can be done without creating side thrust on the shaft that might cause it ,tol bind, or at least turn and slide with considerable friction in the bushing, because the side thrust is balanced or nearly counteracted by meansV of a compression spring 2S that is located in front of the coil spring-and compressed between the side wall of the switch housing and the side of the control shaft. By'pushing laterally against the shaft in one direction, this spring prevents the coil spring from pulling the shaft oif center in the opposite direction. The stronger the coil spring, the stronger the compression spring should be.

The compression spring preferably is triangularand formed from a wire that has astraight central portion extending entirely across the housing and the shaft, and converging end portions provided with free ends engaging the side `of the housing. In fact, these ends may'actually dig into the side wall. It will be seen that the compression spring is restrained by the control shaftand housing side wall from b odily movement in the plane of the spring.v The spring is held against the front wall of the housing by lugs 26 projecting from the two tongues 19 and overlying the straight central portion of the spring. The compression spring also provides a very good electrical connection between the control shaft Vand the switch housing and thereby insures good grounding of the shaft.

Another advantage of compression spring is that it can serve to limit forward movement of the control shaft ,4 in the switch. This is done by providing the rear end portion of the shaft with an integral enlargement 27 that will strike the compression spring when the control shaft has been pulled forward a predetermined distance. The spring makes it easy to assemble the shaft with the switch housing because, after the spring has been put in place, the `shaft can be pushed back through opening 8, with the rearwardly tapered enlargement 27 deflecting the spring laterally until the spring can snap back in front of the enlargement, thereby locking the shaft in the switch housing. If desired, the spring can also be used for limiting backward or inward movement of the control shaft, which can be provided with a shoulder 28 to engage the spring when the shaft has been pushed in the required distance.

In the embodiment of the invention shown in Figs. 7 and 8, other ways that the switch can be made are shown. The oscillatable switch arm 30 can be Vsplit between its central opening and its free end and each fork 31 thus formed can be provided Iwith a oating bridging contact 32 like the one already described, but shorter. Each of these contacts can be swung back against a different pair of fixed contacts 3:3y mounted in the rear wall 34 of the switch housing 35. Due to the arm being forked, each bridging contact can engage its pair of iixed contacts without interference from the other set of contacts. That is, one fork of the arm can flex slightly relative to the other fork so that both bridging contacts will engage their xed contacts with uniform pressure.

This embodiment of the invention also illustrates auother feature, which is that the opposite end of arm 30 can be provided with one or more contacts 36 for engaging fixed contacts 37 at that side of the housing. It will be seen that contact '36 will engage contacts 37 when the contacts at the opposite end of the arm are open. There are electric circuits in which such a system is desirable.

According to the provisions of the patent statutes, I have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be'practiced otherwise than as specifically illustrated and described.

I claim:

1. A push-pull electric switch comprising a housing having front and back walls connected by a side wall, the front wall having a central opening through it, a bushing rigidly mounted in front of the front wall in line with said opening, a control shaft rotatably and slidably mounted in the bushing and extending back into the housing, a switch arm inside the housing inclined to the shaft and provided with an opening loosely receiving the shaft extending therethrough, means oscillatably mounting the arm on an axis extending across the shaft, a coil spring tensioned between the rear end of the shaft and one endv of the arm, the point of connection of the shaft to the spring being movable by the shaft forward from a location in back of said axis to a location in front ofV said axis to cause the spring to snap said end of the arm forward and thereby swing its opposite free end backward toward said back wall, an electric contact carried by the free end of the arm, a fixed electric contact mounted in the housing in position to be engaged by the other `contact when it is swung toward the fixed contact, and a spring in-the housing in front of the coil spring and cornpressed between the housing side wall and the side of the shaft to substantially counteract the lateral tension exerted on the shaft by the coil spring. Y

2. A switch according to claim l, including means projecting from the housing and overlying said compression spring to hold it against the front wall of Vthe housing..

3. A switch accordingY to claim 1, in which said corn-` pression spring has` a portion extending across the shaft, and the shaft is provided with a lateral projection behind Said spring portion for engaging it to limit forward movement of the shaft when the shaft is pulled.

4. A switch according to claim 1, in which said free end of the arm is forked and said arm contact is carried by one fork, a second contact is carried by the other fork, and an Iadditional xed contact is mounted in the housing in position to be engaged by said second contact Whenit is swung toward the additional fixed contact.

5. A switch according to claim 1, including a second contact carried by said one end of the arm, and a fixed contact mounted in the housing in position to be engaged by said second contact when the free end of the arm is swung forward.

6. A switch according to claim 1, in which there are two fixed contacts mounted in the housing and said arm contact is a bridging bar loosely connected to the arm so that it can adjust itself to said fixed contacts.

7. A switch according to claim l, in which said fixed contact is of general L-shape with one leg of the L extending through the back wall of the housing and the other leg extending along the back wall inside the housing.

8. A push-pull electric switch comprising a housing having front and baok walls connected by a side wall, the front wall having a central opening through it, a lbushing rigidly mounted in front of the front wall in line with said opening, a control shaft rotatably and slidably mounted in the bushing and extending back into the housing, a switch arm inside the housing inclined to the shaft and provided with an opening loosely receiving the shaft extending therethrough, means oscillatably mounting the arm on an axis extending across the shaft, a coil spring tensioned between the rear end of the shaft and one end of the arm, the point of-connection of the shaft to the spring being movable by the shaft* forward from a location in back of said axis to a location in front of s'aid axis to cause the spring to snap said end of the arm forward and thereby swing its opposite free end backward toward said back wall, an electric contact carried by the free end of the arm, a fixed electric contact mounted in the housing in position to be engaged by the other contact when it is swung toward the fixed contact, and a wire spring in the housing in front of the coil spring, the wire spring having a central body extending across the housing in engagement with the side o-f the shaft and having converging end portions terminating in ends pressing against the housing side wall hard enough to cause the wire spring to substantially balance the lateral pull of the coil spring on the shaft.

9. A switch according to claim 4, including lugs in the housing connected with the front wall of the housing at opposite sides of the shaft and overlying said spring body to hold it against the front Wall of the housing.

10. A push-pull electric switch comprising a housing having front and back walls connected by a side wall, the front wall having a central opening through it, a bushing rigidly mounted in front of the front wall in line with said opening, a control shaft rotatably and slidably mounted in the bushing and extending back into the housing, a switch arm inside the housing inclined to the shaft and provided with an opening loosely receiving the shaft extending therethrough, bearing members projecting rearward from the front wall of the housing at opposite sides of the shaft, said arm being provided with transverse shoulders engaging one side of said members and adapted to rock thereon on an axis extending across the shaft, a coil spring tensioned between the rear end of the shaft and the end of the arm at said side of the bearing members to hold said shoulders against those members, the point of connection of the shaft to the spring being movable by the shaft forward from a location in back of said shoulders to a location in front of them to cause the spring to snap said end of the arm forward and thereby swing its opposite free end backward toward said back wall, an electric contact carried by the .free end of the arm, a fixed electric contact mounted in the housing in position to be engaged by the other contact when it is swung toward the fixed contact, and a spring in the housing in front of the coil spring and compressed between the housing side wall and the side of the shaft to substantially counteract the lateral tension exerted on the shaft by the coil spring.

11. A switch according to claim 10, in which said arm opening is substantially T-shape, said coil spring being disposed in the stem of the T and said shoulders being located where the stern joins the cross bar of the T, said bearing members projecting through said arm opening at the opposite ends of its cross bar portion.

12. A push-pull electric switch comprising a housing having front and back walls connected by a side wall, the front wall being sheet metal and having a central opening through it, a bushing rigidly mounted in front of the front wall in line with said opening, a control shaft rotatably and slidably mounted in the bushing and extending back into the housing, a switch arm inside the housing inclined to the shaft and provided with an opening loosely receiving the shaft extending therethrough, the central portion o-f said arm being provided with laterally spaced transverse shoulders, substantially parallel tongues in the housing struck out of said front wall at opposite sides of the shaft and having notched edges receiving said shoulders, a coil spring tensioned between the rear end of the shaft and the end of the arm at the notched side of rthe tongues to hold said shoulders against the tongues, the point of connection of the shaft to the spring being movable by the shaft forward from a location in back of said shoulders to a location in front of them to cause the spring to snap said end of the arm forward and thereby swing its opposite free end backward toward said baok wall, a xed electric contact mounted in the housing in position to be engaged by the other contact when it is swung toward the fixed contact, and a spring in the housing in front of the coil spring and compressed between the housing side wall and the side of the shaft to substantially counteract the lateral tension exerted on the shaft by the coil spring.

13. A switch according to claim 12, in which said compression spring has a portion extending across Said tongues, and lugs project from the tongues directly behind said spring portion to hold it against the front wall of the housing.

References Cited in the file of this patent UNITED STATES PATENTS 2,844,676 Barder et al. July 22, 1958 

